The document discusses software process models and activities. It introduces generic process models like waterfall, evolutionary development, and component-based development. It also covers the Rational Unified Process model and its phases. Finally, it discusses various software engineering activities like specification, design, implementation, testing, and evolution as well as the role of computer-aided software engineering tools in supporting software processes.

1. 1
Chapter 2
Software Processes
An overview of conventional software
process models, Rational Unified
Process, and CASE tools

2. 2
Objectives
 To introduce software process models
 To describe three generic process models
and when they may be used
 To describe outline process models for
requirements engineering, software
development, testing and evolution
 To explain the Rational Unified Process
model
 To introduce CASE technology to support
software process activities

3. 3
Topics covered
 Software process models
 Process iteration
 Process activities
 The Rational Unified Process
 Computer-aided software engineering

4. 4
The software process
 A structured set of activities required to develop a
software system
 Specification;
 Design;
 Validation;
 Evolution.
 A software process model is an abstract
representation of a process. It presents a
description of a process from some particular
perspective.

5. 5
Generic software process models
 The waterfall model
 Separate and distinct phases of specification and
development.
 Evolutionary development
 Specification, development and validation are
interleaved.
 Component-based software engineering
 The system is assembled from existing components.
 There are many variants of these models e.g. formal
development where a waterfall-like process is used
but the specification is a formal specification that is
refined through several stages to an implementable
design.

6. 6
Waterfall model

7. 7
Waterfall model phases
 Requirements analysis and definition
 System and software design
 Implementation and unit testing
 Integration and system testing
 Operation and maintenance
 The main drawback of the waterfall model is the
difficulty of accommodating change after the
process is underway. One phase has to be
complete before moving onto the next phase.

8. 8
Waterfall model problems
 Inflexible partitioning of the project into distinct
stages makes it difficult to respond to changing
customer requirements.
 Therefore, this model is only appropriate when the
requirements are well-understood and changes will
be fairly limited during the design process.
 Few business systems have stable requirements.
 The waterfall model is mostly used for large
systems engineering projects where a system is
developed at several sites.

9. 9
Evolutionary development
 Exploratory development
 Objective is to work with customers and to evolve
a final system from an initial outline specification.
Should start with well-understood requirements
and add new features as proposed by the
customer.
 Throw-away prototyping
 Objective is to understand the system
requirements. Should start with poorly understood
requirements to clarify what is really needed.

10. 10
Evolutionary development

11. 11
Evolutionary development
 Problems
 Lack of process visibility;
 Systems are often poorly structured;
 Special skills (e.g. in languages for rapid
prototyping) may be required.
 Applicability
 For small or medium-size interactive systems;
 For parts of large systems (e.g. the user interface);
 For short-lifetime systems.

12. 12
Component-based software engineering
 Based on systematic reuse where systems
are integrated from existing components or
COTS (Commercial-off-the-shelf) systems.
 Process stages
 Component analysis;
 Requirements modification;
 System design with reuse;
 Development and integration.
 This approach is becoming increasingly used
as component standards have emerged.

13. 13
Reuse-oriented development

14. 14
Process iteration
 System requirements ALWAYS evolve in the
course of a project so process iteration
where earlier stages are reworked is always
part of the process for large systems.
 Iteration can be applied to any of the generic
process models.
 Two (related) approaches
 Incremental delivery;
 Spiral development.

15. 15
Incremental delivery
 Rather than deliver the system as a single
delivery, the development and delivery is broken
down into increments with each increment
delivering part of the required functionality.
 User requirements are prioritised and the highest
priority requirements are included in early
increments.
 Once the development of an increment is started,
the requirements are frozen though requirements
for later increments can continue to evolve.

16. 16
Incremental development

17. 17
Incremental development advantages
 Customer value can be delivered with each
increment so system functionality is available
earlier.
 Early increments act as a prototype to help
elicit requirements for later increments.
 Lower risk of overall project failure.
 The highest priority system services tend to
receive the most testing.

18. 18
Extreme programming
 An approach to development based on the
development and delivery of very small
increments of functionality.
 Relies on constant code improvement, user
involvement in the development team and
pairwise programming.
 Covered in Chapter 17

19. 19
Spiral development
 Process is represented as a spiral rather
than as a sequence of activities with
backtracking.
 Each loop in the spiral represents a phase in
the process.
 No fixed phases such as specification or
design - loops in the spiral are chosen
depending on what is required.
 Risks are explicitly assessed and resolved
throughout the process.

20. 20
Spiral model of the software process

21. 21
Spiral model sectors
 Objective setting
 Specific objectives for the phase are identified.
 Risk assessment and reduction
 Risks are assessed and activities put in place to
reduce the key risks.
 Development and validation
 A development model for the system is chosen which
can be any of the generic models.
 Planning
 The project is reviewed and the next phase of the
spiral is planned.

22. 22
Process activities
 Software specification
 Software design and implementation
 Software validation
 Software evolution

23. 23
Software specification
 The process of establishing what services
are required and the constraints on the
system’s operation and development.
 Requirements engineering process
 Feasibility study;
 Requirements elicitation and analysis;
 Requirements specification;
 Requirements validation.

24. 24
The requirements engineering process

25. 25
Software design and implementation
 The process of converting the system
specification into an executable system.
 Software design
 Design a software structure that realises the
specification;
 Implementation
 Translate this structure into an executable
program;
 The activities of design and implementation
are closely related and may be inter-leaved.

26. 26
Design process activities
 Architectural design
 Abstract specification
 Interface design
 Component design
 Data structure design
 Algorithm design

27. 27
The software design process

28. 28
Structured methods
 Systematic approaches to developing a
software design.
 The design is usually documented as a set of
graphical models.
 Possible models
 Object model;
 Sequence model;
 State transition model;
 Structural model;
 Data-flow model.

29. 29
Programming and debugging
 Translating a design into a program and
removing errors from that program.
 Programming is a personal activity - there is
no generic programming process.
 Programmers carry out some program
testing to discover faults in the program and
remove these faults in the debugging
process.

30. 30
The debugging process

31. 31
Software validation
 Verification and validation (V & V) is intended
to show that a system conforms to its
specification and meets the requirements of
the system customer.
 Involves checking and review processes and
system testing.
 System testing involves executing the system
with test cases that are derived from the
specification of the real data to be processed
by the system.

32. 32
The testing process

33. 33
Testing stages
 Component or unit testing
 Individual components are tested
independently;
 Components may be functions or objects or
coherent groupings of these entities.
 System testing
 Testing of the system as a whole. Testing of
emergent properties is particularly important.
 Acceptance testing
 Testing with customer data to check that the
system meets the customer’s needs.

34. 34
Testing phases

35. 35
Software evolution
 Software is inherently flexible and can change.
 As requirements change through changing
business circumstances, the software that
supports the business must also evolve and
change.
 Although there has been a demarcation
between development and evolution
(maintenance) this is increasingly irrelevant as
fewer and fewer systems are completely new.

36. 36
System evolution

37. 37
The Rational Unified Process
 A modern process model derived from the
work on the UML and associated process.
 Normally described from 3 perspectives
 A dynamic perspective that shows phases over
time;
 A static perspective that shows process activities;
 A practive perspective that suggests good
practice.

38. 38
RUP phase model
Phase iteration
Inception Elaboration Construction Transition

39. 39
RUP phases
 Inception
 Establish the business case for the system.
 Elaboration
 Develop an understanding of the problem domain
and the system architecture.
 Construction
 System design, programming and testing.
 Transition
 Deploy the system in its operating environment.

40. 40
inception
Rational Unified Process
software increment
Release
Inception
Elaboration
construction
transition
production
inception
elaboration

41. 41
RUP Phases
Inception Elaboration Construction Transition Production
UP Phases
Workflows
Requirements
Analysis
Design
Implementation
Test
Iterations #1 #2 #n-1 #n
Support

42. 42
RUP Work Products
Inception phase
Elaboration phase
Construction phase
Transition phase
Vision document
Init ial use-case model
Init ial project glossary
Init ial business case
Init ial risk assessment .
Project plan,
phases and it erat ions.
Business model,
if necessary.
One or more prot ot ypes
I nc e pt i o
n
Use-case model
Supplement ary requirement s
including non-funct ional
Analysis model
Soft ware archit ect ure
Descript ion.
Execut able archit ect ural
prot ot ype.
Preliminary design model
Revised risk list
Project plan including
it erat ion plan
adapt ed workflows
milest ones
t echnical work product s
Preliminary user manual
Design model
Soft ware component s
Int egrat ed soft ware
increment
Test plan and procedure
Test cases
Support document at ion
user manuals
inst allat ion manuals
descript ion of current
increment
Delivered soft ware increment
Bet a t est report s
General user feedback

43. 43
RUP good practice
 Develop software iteratively
 Manage requirements
 Use component-based architectures
 Visually model software
 Verify software quality
 Control changes to software

44. 44
Static workflows
Workflow Description
Business modelli ng The business processes are modelled usingbu siness use cases.
Requirements Actors who interact with the system are identified and use cases are
developed to model the system requirements.
Ana lysis and de sign A design model is created and do cumented usinga rchitectural
models, component models, object models and sequence mod els.
Implementation The components in the system are implemented and structured into
implementation sub-systems. Automatic code generation from design
models helps accelerate this process.
Test Testing is an iterative process that is carried out inconjunc tion with
implementation. System testing follows the completion of the
implementation.
Deployment A produc t release is created, distributed to users and installed in their
workplace.
Configurationand
chang e management
This supporting workflow managed change s to the system (see
Chapter 29).
Project management This supporting workflow manage s the system development (see
Chapter 5).
Envi ronment This workflow is concerned with making appropriate software tools
available to the software development team.

45. 45
Specification
Acquisition
Specification
Validation
Maintenance
high-level
specification
(prototyping)
Interactive
Translation
Automatic
Compilation
source
program
informal
specification
decision &
rational
low-level
specification
formal
development
Tuning
Automated Synthesis Model

46. 46
longevity
t0 t1 t2 t3 t4 t5
Functionality
Time
inappropriateness
lateness
shortfal
l slop : adaptability
original reqt.
A
B
D
C
E
waterfall
model
O : (t0) original reqt.
A : ( at t1) an operational product, not satisfying the old to needs
because poor understanding of needs.
A - B : undergo a series of enhancements.
B - D : the cost of enhancements increase, to build a new system.
stop at t4.
* cycle repeat itself
Comparing Various Process Models

47. 47
before understanding
of the user`s need =>
increase in functionality
t0 t1 t2 t4
Functionality
Time
Throwaway Prototyping and Spiral Model

48. 48
Time
t0 t1 t2 t4
Functionality
Evolutionary Prototyping

49. 49
t0 t1 t2 t4
Functionality
t3
Time
Automated Software Synthesis

50. 50
t0 t1 t2 t4
Functionality
Time
user
Reusable Software
approach
conventional
approach
Reusable Software versus Conventional

51. 51
Computer-Aided Software Engineering
 Computer-Aided Software Engineering (CASE) is
software to support software development and
evolution processes.
 Activity automation
 Graphical editors for system model development;
 Data dictionary to manage design entities;
 Graphical UI builder for user interface construction;
 Debuggers to support program fault finding;
 Automated translators to generate new versions of a
program.

52. 52
CASE technology
 CASE technology has led to significant
improvements in the software process.
However, these are not the order of
magnitude improvements that were once
predicted
 Software engineering requires creative thought -
this is not readily automated;
 Software engineering is a team activity and, for
large projects, much time is spent in team
interactions. CASE technology does not really
support these.

53. 53
CASE classification
 Classification helps us understand the different
types of CASE tools and their support for process
activities.
 Functional perspective
 Tools are classified according to their specific function.
 Process perspective
 Tools are classified according to process activities that
are supported.
 Integration perspective
 Tools are classified according to their organisation into
integrated units.

54. 54
Functional tool classification
Tool type Examples
Planning tools PERT tools, estimation tools, spreadsheets
Editing tools Text editors, diagram editors, word processors
Change management tools Requirements traceability tools, change control systems
Configuration management tools Version management systems, systembuilding tools
Prototyping tools Very high-level languages, user interface generators
Method-support tools Design editors, data dictionaries, code generators
Language-processing tools Compilers, interpreters
Program analysis tools Cross reference generators, static analysers, dynamic analysers
Testing tools Test data generators, file comparators
Debugging tools Interactive debugging systems
Documentation tools Page layout programs,image editors
Re-engineering tools Cross-reference systems, program re-structuring systems

55. 55
Activity-based tool classification
Specification Design Implementation V
erification
and
V
alidation
Re-eng ineering tools
Testing tools
Debugg ing tools
Program analysis tools
Language-processing
tools
Method suppor t tools
Prototyping tools
Configuration
management tools
Change management tools
Documentation tools
Editing tools
Planning tools

56. 56
CASE integration
 Tools
 Support individual process tasks such as design
consistency checking, text editing, etc.
 Workbenches
 Support a process phase such as specification or design,
Normally include a number of integrated tools.
 Environments
 Support all or a substantial part of an entire software
process. Normally include several integrated workbenches.

57. 57
Tools, workbenches, environments
Single-method
workbenches
Gener al-purpose
workbenches
Multi-method
workbenches
Langua ge-specific
workbenches
Programming T
esting
Analysis and
design
Integrated
envir
onments
Process-centr ed
envir
onments
File
compar ators
Compilers
Editors
Envir
onments
Workbenches
T
ools
CASE
technology

58. 58
Key points
 Software processes are the activities involved in
producing and evolving a software system.
 Software process models are abstract
representations of these processes.
 General activities are specification, design and
implementation, validation and evolution.
 Generic process models describe the organisation
of software processes. Examples include the
waterfall model, evolutionary development and
component-based software engineering.
 Iterative process models describe the software
process as a cycle of activities.

59. 59
Key points
 Requirements engineering is the process of
developing a software specification.
 Design and implementation processes transform the
specification to an executable program.
 Validation involves checking that the system meets
to its specification and user needs.
 Evolution is concerned with modifying the system
after it is in use.
 The Rational Unified Process is a generic process
model that separates activities from phases.
 CASE technology supports software process
activities.